1. Field of the Invention
This invention relates to a magnetostatic wave device and, more particularly, to a magnetostatic wave device which comprises a ferromagnetic element such as a YIG (yttrium iron garnet) element, a magnet for applying a magnetic field to the ferromagnetic element, and transducers provided in conjunction with the ferromagnetic element.
2. Description of the Prior Art
FIG. 11 is an illustrative sectional view showing one example of the conventional magnetostatic wave devices which is disclosed in Japanese Utility Model Application No. 148370/1989 (Japanese Utility Model Provisional Publication No. 86601/1991). The magnetostatic wave device 1 includes a chassis 2 made of metal, and in the chassis 2, a dielectric substrate 3 made of, for example, alumina is provided midway along the height of a chassis. On the undersurface of the dielectric substrate 3, a YIG element 4 of, for example, a strip is provided, and under the YIG element 4, an earth plate 5 is disposed. Furthermore, on the top face of the dielectric substrate 3, two spaced apart transducers (not shown) are provided. These transducers are respectively connected to two coaxial connectors (not shown) which penetrate a side wall of the chassis 2.
Furthermore, in the chassis 2, magnets 6a and 6b for applying a d.c. magnetic field to the YIG element 4 are disposed with the dielectric substrate 3 between them.
In the magnetostatic wave device 1, for example, when a signal is applied to one transducer by inputting the signal to one coaxial connector, the signal is excited as a magnetostatic forward volume wave (MSFVW). The magnetostatic forward volume wave is propagated toward the other transducer on the YIG element 4 and received by the transducer to output it as a signal from the other coaxial connector.
Furthermore, into the top wall of the chassis 2 of the magnetostatic wave device 1, two adjusting screws 7a and 7b are driven. These adjusting screws 7a and 7b are for adjusting a distribution of a magnetic field applied to the YIG element 4. Still furthermore, into the bottom wall of the chassis 2, another adjusting screw 8 is threaded, at the end of which another magnet 9 is fixed. The adjusting screw 8 and magnet 9 are for varying a magnitude of a magnetic field applied to the YIG element 4 to vary a frequency characteristic of the magnetostatic wave device 1.
However, in the magnetostatic wave device 1, a spacing between the two magnets 6a and 6b and a spacing between the chassis 2 and the magnet 6a must be kept at predetermined distances, and it is difficult to position the YIG element, the magnets and the transducers and thus the device has inferior workability and productivity when assembled.
The inventors of the present invention have proposed that the ferromagnetic element, the magnet and the transducers are housed in a metal holder in order to facilitate positioning of them, but this results in a heavy weight of the whole device.